| Summary: | Silver chloride crystals containing different transition metal ions have been investigated by electron spin resonance spectroscopy. The properties of iron impurity have been studied in detail. The irradiation of crystals containing divalent iron leads to the formation of a trigonal trivalent complex when the temperature of the crystal is about 170 degrees K. Subsequent warming of the crystal to 200 degrees K converts this complex into the cubic centre which has been identified by Hayes, Pilbrow and Slifkin. A model is proposed for the trigonal spectrum and a mechanism is suggested for the processes which occur in the crystal during and after irradiation. A number of other spectra have been observed, but owing to difficulties in reproducing these, it is only possible to make general comments regarding their classification and origin. The S-state spectra for both the cubic and the trigonal sites exhibit some unusual characteristics which are discussed in some detail. Single crystal experiments have been carried out on a 1OOKc/s field modulation, X-band spectrometer at 20 degrees K, 77 degrees K and at 300 degrees K. The e.s.r. spectrometer is conventional apart from the absorption cell which is a standing wave helix rather than a microwave cavity. The use of a helix in an e.s.r. spectrometer is described, and ideal design criteria are calculated to take account of dielectric loading of the helix by non-lossy samples. The spectrometer sensitivity is comparable with a similar cavity instrument, principally because of the high filling factor which can be obtained.
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